Combustor having an acoustically enhanced ejector system

ABSTRACT

The present specification generally relates to improvements to combustors such as burners and engines. In one aspect, the specification presents an acoustically enhanced ejector system which can be used as part of an intake system for a combustor. In another aspect, the specification teaches the use of a combustor combustion chamber as an oscillator to magnify a harmonic frequency of a pulsating frequency of the combustor. In still other aspects, the specification presents a combustion chamber having an inlet with a plurality of tangentially spaced apertures, and an in-line intake system connected to the apertures.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional of U.S. patent application Ser.No. 11/994,690, filed Jan. 4, 2008, now U.S. Pat. No. 8,083,494 which isthe National Stage of International Application No. PCT/CA2006/000950,filed Jun. 8, 2006 which claims priority to U.S. provisional patentapplication No. 60/695,888, filed Jul. 5, 2005; U.S. provisional patentapplication No. 60/706,006 filed Aug. 8, 2005; and Canadian patentapplication no. 2,512,937, filed Jul. 28, 2005; all of which are herebyincorporated by reference.

FIELD

The improvements relates to the field of combustors, and moreparticularly to combustors for use as burners or as engines.

BACKGROUND

Pulse combustors have been known for many years. They work on theprinciple that a load of mixed fuel and air periodically enters acombustion chamber where it ignites, therefore giving a pulsecombustion. Some pulse combustors are specifically adapted for use asburners. Other pulse combustors are specifically adapted for use asengines of the pulse-jet type. Typical pulse-jet engines use valveswhich periodically allow fuel and air intake. There is a general need inthe field of pulse combustors to enhance efficiency, durability andthrust output of pulse combustors.

U.S. Pat. No. 3,093,962 to Gluhareff teaches a valveless pulse-jetengine and somewhat discusses the use of acoustics. There is a need inthe art to somewhat elaborate on the teachings of Gluhareff.

Furthermore, known pulse combustors are typically limited to a pulsemode of combustion.

SUMMARY

An aim of the improvements is to alleviate some of the needs concerningcombustors.

In accordance with one aspect, the improvements provide an ejectorsystem comprising: a supersonic fluid injection nozzle having anacoustic injection frequency and amplitude; a first resonant tube havingan inlet coupled to the nozzle for receiving the injected fluid from thenozzle and ambient fluid entrained by the injected fluid, and an outletfor ejecting the fluids, the first resonant tube having a firstfundamental resonance frequency excitable by the nozzle injection; and asecond resonant tube having an inlet coupled to receive the fluidsejected from the outlet of the first resonant tube outlet for receivingthe ejected fluids and additional ambient fluid entrained by the ejectedfluids, and an outlet for ejecting the fluids received by the inlet, thesecond resonant tube having a second fundamental resonance frequencybeing a sub-harmonic of the first fundamental resonance frequency.

In accordance with an other aspect, the improvements provide an ejectorsystem having a first resonant tube having a first fundamental resonancefrequency, an inlet and an outlet, a second resonant tube wider than thefirst resonant tube having a second fundamental resonance frequency, aninlet coupled to the outlet of the first resonant tube, and an outlet,and a supersonic fluid nozzle aerodynamically coupled to the inlet ofthe first resonant tube, the supersonic fluid nozzle having an acousticinjection frequency and amplitude suitable to acoustically excite thefirst and the second resonant tubes, the ejector system beingCHARACTERIZED IN THAT the first resonance frequency is a harmonic of thesecond resonance frequency.

In accordance with an other aspect, the improvements provide an intakesystem for a combustor having a pulsating frequency, the intake systemcomprising: a supersonic injection fuel nozzle having an acousticinjection frequency and amplitude; a first resonant tube having an inletcoupled to the nozzle for receiving the injected fuel and ambient airentrained by the injected fuel, and an outlet for ejecting the fuel andthe air, the first resonant tube having a first fundamental resonancefrequency excitable by the fuel nozzle; a second resonant tube having aninlet coupled to the outlet of the first resonant tube for receiving theejected fuel and air and additional ambient air entrained by the ejectedfuel and air, and an outlet, the second resonant tube having a secondfundamental resonance frequency being a sub-harmonic of the firstfundamental resonance frequency; and a resonant intake tube having aninlet coupled to the outlet of the second resonant tube for receivingthe fluids ejected from the second resonant tube outlet and additionalambient fluid entrained by these ejected fluids, and an outlet connectedto a combustion chamber inlet of the combustor.

In some cases, the combustor further has a resonator having afundamental resonance frequency which corresponds to the pulsatingfrequency, the resonator further having the combustion chamber inlet, anoutlet, an oscillator for use as the combustion chamber, having theinlet at an acoustic center thereof and defining one end of theresonator, and an exhaust pipe extending from the oscillator and havingthe outlet at the opposite end of the resonator, wherein the oscillatorhas a resonance frequency which is an odd harmonic of the pulsatingfrequency and at least one of the coupling between the first resonanttube and the second resonant tube and the coupling between the secondresonant tube and the intake tube has a difference of area and apenetration depth suitable for the intake system to define a high-passfilter having a cut-off frequency between the pulsating frequency andthe oscillator fundamental frequency.

In some cases, the odd harmonic is the third harmonic.

In accordance with an other aspect, the improvements provide a method ofejecting fluid, the method comprising: making high frequency noise byinjecting one of an over-expanded and under-expanded supersonic flow offluid into a first resonant tube at a speed sufficient for the fluidmomentum to entrain ambient fluid through the first tube, and for thefluid exiting the first tube to entrain further air particles through asecond tube; and driving the first tube into resonance using the highfrequency noise, and driving the second tube into resonance using theresonance of the first tube.

In some cases, the ejected fluid is fuel and the ambient fluid is air.

In accordance with an other aspect, the improvements provide an acousticcavity for use in a combustor having a pulsating frequency, the acousticcavity comprising: a resonator with a fundamental resonance frequencywhich corresponds to the pulsating frequency of the combustor, theresonator further having an inlet, and an outlet; an oscillator madeintegral to the resonator and defining one end thereof, being for use asa combustion chamber, having a fundamental resonance frequency which isan odd harmonic of the pulsating frequency and having the inlet at anacoustic center thereof, and an exhaust pipe made integral to theresonator and having the outlet at an opposite end thereof, the exhaustpipe extending from the oscillator.

In accordance with an other aspect, the improvements provide a combustorcomprising: a resonator having a fundamental resonance frequency whichcorresponds to a pulsating frequency of the combustor when operating ina pulse mode, the resonator further having: an oscillator for use as acombustion chamber, having a fundamental resonance frequency which is anodd harmonic of the pulsating frequency, and having an inlet at anacoustic center thereof, the oscillator defining one end of theresonator, and an exhaust pipe extending from the oscillator and havingan outlet at the opposite end of the resonator; and an intake systemconnected to the inlet to feed the combustion chamber with fuel and air.

In accordance with an other aspect, the improvements provide an acousticcavity for use in a combustor having a pulsating frequency, the acousticcavity having a resonator with a fundamental resonance frequency whichcorresponds to the pulsating frequency of the combustor, the resonatorfurther having an inlet, an outlet, an oscillator for use as acombustion chamber, having the inlet at an acoustic center thereof anddefining one end of the resonator, and an exhaust pipe extending fromthe oscillator and having the outlet at the opposite end of theresonator, the acoustic cavity being CHARACTERIZED IN THAT theoscillator has a fundamental resonance frequency which is an oddharmonic of the pulsating frequency.

In accordance with an other aspect, the improvements provide a combustorhaving a resonator with a fundamental resonance frequency, the resonatorfurther having an inlet and an outlet, and a combustion chamber oppositethe outlet, the combustion chamber defining an oscillator and having theinlet at an acoustic center thereof, the combustor further having anintake system connected to the inlet, the combustor being CHARACTERIZEDIN THAT the oscillator has a fundamental resonance frequency which is aharmonic of the resonator fundamental frequency, the intake system isacoustically excitable by the oscillator fundamental frequency, and theintake system defines an acoustic high-pass filter to reflect theresonator fundamental frequency back into the combustion chamber.

In accordance with an other aspect, the improvements provide a method ofpulsatingly combusting fuel in a resonator at a fundamental resonancefrequency of the resonator, the method comprising: magnifying a harmonicfrequency of the fundamental resonance frequency in a combustion chamberportion of the resonator; exciting an acoustic high-pass filter definedby an intake system connected to the combustion chamber with themagnified harmonic frequency; impeding the transmission of the pressurepulses from the fundamental resonance frequency to the intake systemwith the excited acoustic high-pass filter; and feeding fuel and airinto the combustion chamber with the intake system; and periodicallyincreasing the pressure in the combustion chamber by the resonance ofthe resonator.

In accordance with an other aspect, the improvements provide a combustorhaving a main longitudinal axis and a pulsating frequency, the combustorcomprising: a tubular combustor body having an outlet, a combustionchamber opposite the outlet and an exhaust pipe narrower than thecombustion chamber between the combustion chamber and the outlet, thecombustion chamber, exhaust pipe and outlet being in flow communicationalong the main longitudinal axis, and the body having a resonancefrequency corresponding to the pulsating frequency; a plurality ofsubstantially longitudinally oriented slots interspaced around thecombustion chamber at a longitudinal acoustic center thereof, the slotsdefining an inlet to the body; and an intake system connected to thecombustion chamber inlet.

In accordance with an other aspect, the improvements provide a combustorhaving an elongated combustion chamber having an inlet proximate alongitudinal center thereof, an intake system connected to thecombustion chamber inlet, and a tail pipe extending from the combustionchamber and defining an outlet thereto, wherein the combination of thecombustion chamber and the tail pipe define an acoustic resonator havinga fundamental resonance frequency at which fuel from the intake systemis to be pulsatingly ignited in the combustion chamber, the combustorbeing CHARACTERIZED IN THAT the inlet comprises a plurality oflongitudinally oriented slots being peripherally interspaced around thecombustion chamber.

In accordance with an other aspect, the improvements provide a combustorcomprising: a tubular combustor body, the body having: a combustionchamber having a plurality of tangentially spaced apertures, and anexhaust pipe narrower than the combustion chamber and extending awayfrom the combustion chamber and being in flow communication therewith,the exhaust pipe defining an outlet of the tubular combustor body; andan intake system connected to the apertures to feed the combustionchamber with fuel and air.

In some cases, the apertures are disposed in a peripheral surface of thecombustion chamber. In other cases, the apertures are disposed around anintake tube which protrudes into the combustion chamber.

In accordance with an other aspect, the improvements provide a combustorhaving a main longitudinal axis comprising: a tubular combustor bodyhaving an outlet, a combustion chamber portion opposite the outlet andan exhaust pipe narrower than the combustion chamber between thecombustion chamber and the outlet, the combustion chamber portion,exhaust pipe and outlet being disposed along the main longitudinal axis,and the body having a resonance frequency corresponding to a pulsatingfrequency of the combustor; an intake system having an intake tubelongitudinally penetrated into the combustion chamber along the mainaxis, opposite the outlet, the intake tube having an open end outsidethe combustion chamber, a closed end inside the combustion chamber, andplurality of longitudinally oriented apertures tangentially interspacedaround the intake tube at a longitudinal acoustic center of thecombustion chamber, the slots defining an inlet to the combustionchamber.

In accordance with an other aspect, the improvements provide a combustorhaving an elongated combustion chamber having an inlet proximate alongitudinal center thereof, an intake system connected to thecombustion chamber inlet, and an exhaust pipe extending from thecombustion chamber and defining an outlet thereto, wherein thecombination of the combustion chamber and the tail pipe define anacoustic resonator having a fundamental resonance frequency at whichfuel from the intake system is to be pulsatingly ignited in thecombustion chamber, the combustor being characterized in that the intakesystem is aligned on an axis common to the combustion chamber and to theexhaust pipe and that the combustion chamber inlet is peripheral to thecombustion chamber.

In accordance with an other aspect, the improvements provide a turbinesystem for an in-line combustor having an intake system, a body and anoutlet aligned along a combustor axis, the turbine system having a powerturbine adapted to extract energy from the gasses exhausted from theoutlet into rotation, a fan positioned upstream from the intake system,and a shaft connecting the power turbine to the shaft, whereby energyfrom the exhausted gasses is transmitted from the power turbine to thefan by the rotation of the shaft and the fan thereby enhances the airintake through the intake system.

In accordance with an other aspect, the improvements provide a method oftuning a combustor having a body defining a resonator and a combustionchamber in the body, the method comprising: selecting a combustionchamber shaped to define an oscillator which has a fundamental resonancefrequency which is the third harmonic of the resonator fundamentalfrequency at operation temperature.

In accordance with an other aspect, the improvements provide a method oftuning an ejector having a high frequency fluid nozzle, a first resonanttube and a second resonant tube, the method comprising: selecting afirst stage resonant tube which has a fundamental resonance frequencywhich is a harmonic of the fundamental resonance frequency of the secondresonant tube.

In the present specification, when reference is made to a resonantfrequency, it is to be understood that what is meant is the resonantfrequency during operation, which may depart from resonant frequency atrest due to temperature variations.

DESCRIPTION OF THE FIGURES

Further features and advantages of the present improvements will becomeapparent from the following detailed description, taken in combinationwith the appended figures, in which:

FIG. 1 is a perspective view of an L-shape pulse combustor in accordancewith the improvements;

FIG. 2 is a cross-sectional view of the pulse combustor of FIG. 1showing the structural elements thereof;

FIG. 3 is a cross-sectional view of the pulse combustor of FIG. 1showing the acoustic elements thereof;

FIG. 4 is a schematic view illustrating variations in pressure over timein the pulse combustor of FIG. 1;

FIG. 5A and FIG. 5B are a side and a top cross-sectional views,respectively, showing the ejector system of the pulse combustor of FIG.1;

FIG. 6 is a perspective view of an in-line combustor in accordance withthe improvements;

FIG. 7 is a cross-sectional view of the combustor of FIG. 6 showing thestructural elements thereof;

FIG. 8 is a cross-sectional view of the combustor of FIG. 6 showing theacoustic elements thereof;

FIG. 9A is a side views, partly sectioned and enlarged, showing theslotted inlet of the combustor of FIG. 6;

FIG. 9B is an enlarged view of the slotted inlet of FIG. 9A;

FIG. 9C is a front cross-sectional view of the slotted inlet of FIG. 9A;

FIG. 9D is a front cross-sectional view of an alternative to the slottedinlet of FIG. 9A;

FIG. 9E is a side cross-sectional view of an alternative to the slottedinlet of FIG. 9A;

FIG. 10 is a side view, partly sectioned, showing the intake system ofthe combustor of FIG. 6;

FIG. 11A, is a side view showing an other configuration of an in-linecombustor in accordance with the improvements;

FIGS. 11B and 11C are cross-section views showing alternateconfigurations of an in-line combustor in accordance with theimprovements;

FIG. 12 is a perspective view showing a turbine engine using a pluralityof in-line combustors; and

FIG. 13 is a perspective view of a Hiller-Lockwood engine having theejector system of FIG. 5A.

DETAILED DESCRIPTION

Referring to the drawings, and more particularly to FIG. 1, an exampleof a pulse combustor 10 having a configuration referred to herein as“L-shaped configuration” is shown. The pulse combustor 10 can be used asa burner to generate a hot air flow and can alternately be used as apulse-jet engine to generate thrust. Typically, when the combustor 10 isused as a burner, it will be mounted to a fixed frame. When it is usedas an engine, it will be mounted to a displaceable vehicle. The pulsecombustor 10 generally includes a body 12 and an intake system 14. Thebody 12 has a generally tubular shape. In the example, the body 12 hasan irregular surface of revolution tubular shape aligned along a mainaxis 16. The intake system 14 will be recognized by those skilled in theart to include an ejector system 18 and is aligned along an intake axis20. The main axis 16 and the intake axis 20 are transverse, thus givingthe L-shape configuration. In the illustrated example, the angle betweenthe main axis 16 and intake axis 20 is of 90 degrees, with the axesbeing in a common plane. Other angles can be used as well.

Referring now to FIG. 2, it is seen that the body 12 includes twoportions: a combustion chamber 22 and an exhaust pipe 24. The body 12has an inlet 26 located in the combustion chamber 22 and an outlet 28 atthe end of the exhaust pipe 24. The combustion chamber 22 is wider thanthe exhaust pipe 24. The combustion chamber 22 includes a nose cone 30opposite to the outlet 28 and having the pointed end outwardly oriented,a converging section 32 bridging the combustion chamber 22 to theexhaust pipe 24 and a generally cylindrical section 34 between the nosecone 30 and the converging section 32. The inlet 26 is located in thecylindrical section 34.

The intake system 14 includes an intake tube 36 having an inlet 36 a andan outlet 36 b, and the outlet 36 b is connected to the combustionchamber inlet 26. In this example, the intake tube 36 is flared anddefines a diverging section between the intake tube inlet 36 a and theintake tube outlet 36 b. This contributes to slowing the gasses enteringthe combustion chamber 22 from the intake system 14. The ejector system18 is coupled to the intake tube inlet 36 a. The ejector system 18includes a supersonic fuel nozzle 38 coupled to the inlet 40 a of afirst tube 40, and a second tube 42 having an inlet 42 a coupled to theoutlet 40 b of the first tube 40. The outlet 42 b of the second tube 42is coupled to the inlet 36 a of the intake tube 36. The intake system 14includes a first tube coupling 44. The first tube coupling 44 includesan adjustment of the relative position between the supersonic fuelnozzle 38 and the first tube 40, and an adjustment of thecross-sectional area of the first tube 40. The intake system 14 alsoincludes a second tube coupling 46 and an intake tube coupling 48.

The tubes 40, 42, 36 of the intake system 14 can be maintained inposition relative to each other in many possible ways. In one examplewhere the combustor is used as a burner, each component of the intakesystem can be mounted to a common frame (not shown). In another examplewhere the combustor is used as an engine, the tubes can be connected toone another with suitable brackets. The exact choice thereof is left tothose skilled in the art.

Those familiar with the principles of ejectors will understand that thecoupling 44 between the nozzle 38 and first tube 40 is such that thefuel exiting the supersonic fuel nozzle 38 at high velocity transferssome of its momentum to adjacent particles of air which entrains a flowof air through the first tube 40 with the flow of fuel. The coupling 46between the first tube 40 and second tube 42 allows fuel and air exitingthe first tube 40 to transfer some of its angular momentum and entrainmore air through the second tube 42. The air mixes with the fuel as ittravels through the first and second tubes. Similarly, the coupling 48between the second tube 42 and the intake tube 36 allows fuel and airexiting the second tube 42 to transfer some of its angular momentum andentrain more air through the intake tube 36 and into the combustionchamber 22.

The mixture of air and fuel entering the combustion chamber 22 ispulsatingly ignited at a pulsating frequency of the pulse combustor 10,and the combustion products are exhausted out the exhaust pipe outlet28. This combustion mode will be referred to herein as the pulse mode.The basic cycle of the pulse mode will be outlined further below withrelation to combustor acoustics.

In this example, the fuel used is gas and can be propane. The supersonicfuel nozzle 38 is adapted to inject such a gaseous fuel. When a gaseousfuel is used, it can be advantageously pre-heated inside the combustionchamber 22. One way to achieve this is to use a coil 50 in thecombustion chamber 22 through which the gaseous fuel circulates prior toreaching the fuel nozzle 38. A fuel source (not shown) is connected to afuel inlet 52. The fuel inlet 52 is connected to the coil 50 through thecombustion chamber wall. The coil 50 has a fuel outlet 54 which exitsthrough the combustion chamber wall and is connected to the fuel nozzle38. During operation of the pulse combustor 10, heat may thus betransferred from the combustion chamber 22 to the fuel through the coil50.

It will be seen from the description below that the acoustics of thepulse combustor 10 is an important consideration in maximizing itsoutput power. It was demonstrated by experiment that the coil 50 has atendency to absorb acoustic vibrations by vibrating, which has beenshown to lower the combustor's efficiency or power output. For thisreason, it can be advantageous to secure the coil 50 to the combustionchamber in a manner to minimize its tendency to vibrate. However, onewill understand that it is practically impossible to entirely eliminatecoil vibration. Resulting coil vibration has a tendency to propagatethrough the material of the conduit connecting the coil outlet 54 to thefuel nozzle 38, especially if this material is rigid. Such vibrationshave been known to negatively influence the injecting action of the fuelnozzle 38. For this reason, it has been found advantageous to use aflexible hose 56 at some point between the coil outlet 54 and the fuelnozzle 38. The flexible hose 56 dissipates energy from the coilvibration and minimizes the amount of vibration which affects the fuelnozzle 38.

It is to be understood that instead of a gaseous fuel, a liquid fuel canbe used with a supersonic fuel nozzle which is adapted to inject aliquid fuel. In this case, there is typically no need to preheat thefuel in the combustion chamber and it is to be understood therefore thatthe coil and flexible hose can be entirely omitted. Such an embodimentis depicted for example in FIG. 3. When selecting a fuel, one mustconsider the flame propagation speed relatively to the pulsatingfrequency and the size of the combustion chamber of the pulse combustor.

At combustor startup, an igniter such as an igniter electrode 58 is usedto start the pulse combustor 10 into operation. In the example, theigniter electrode 58 positioned in the wall of the exhaust pipe 24, nearthe converging section 32 of the combustion chamber 22, is used to startthe combustor 10. However as it will be seen below, once the combustor10 has warmed up, it can be autonomous and maintain its operating cycleby automatically lighting the fuel at the pulsating frequency. At thatpoint, no igniter is necessary to maintain the combustor into operation.For this reason, it is believed that using an igniter which ispermanently part of the combustor is not essential in certainembodiments.

Referring to FIG. 3, a pulse combustor skeleton being quite similar tothat illustrated in FIG. 2 is depicted. One difference between FIG. 2and FIG. 3 lies in the fact that a liquid fuel is used in FIG. 3 insteadof a gaseous fuel, and the coil has therefore been entirely omitted.Apart from that, FIG. 3 is used to illustrate the acoustic components ofthe combustor rather than to focus on the structural, aerodynamic orthermodynamic requirements, since an understanding of the acousticoperating principles of the combustor is useful to understand theimprovements. For clarity, reference numerals in the one hundred serieswill be used to identify corresponding elements in FIG. 3. It will beunderstood by those skilled in the art of acoustics that therequirements to guide pressure waves of sound are much different fromthe requirements to guide fluid mechanics, and that some structuralchanges which may greatly affect the visual geometry of components mayaffect their acoustic behaviour only negligibly.

Referring to FIG. 3, the body 12 and the intake system 14 of the pulsecombustor 10 (FIG. 2) can be seen to define an acoustic cavity 110. Thebody 12 (FIG. 2) acts as an acoustic resonator 112 which may in someways be compared to a closed cylinder air column, and thus bearingresemblance to a wind instrument such as the clarinet. The resonator 112can be said to have a fundamental resonance frequency similar to that ofa closed cylinder air column. The fundamental resonance frequency of theresonator 112 is thus a function of the length of the resonator 112 anda function of the speed of sound. Since the speed of sound is a functionof temperature, and the temperature changes both as a function ofposition and time, the speed of sound varies depending of the positionin the resonator 112. The combustion chamber (22) is typically warmerthan the exhaust pipe (18). The temperature varies over time with theoperating cycle of the combustor, therefore in the instant description,when reference is made to a resonance frequency, it is understood thatwhat is meant is average resonance frequency. This resonance frequencymay be quite different than the resonance frequency at ambienttemperature, especially when referring to the combustion chamber 22,exhaust pipe 24 and intake tube 36.

Typically, the pulsating frequency of the combustor 10 coincides withthe resonator fundamental frequency, although it is envisaged that thecombustor 10 could alternately pulsate at a harmonic of the resonatorfundamental frequency, such as the third harmonic for example. It is theimportant pressure variations at the pulsating frequency in thecombustion chamber that drive the main combustor operating cycle. Forindicative purposes, the pulsating frequency of one example of a pulsecombustor was of about 145 Hz.

In FIG. 4, the pressure variations at pulsating frequency 200 areschematically depicted as a sinusoidal curve, although it is understoodthat the actual pressure variations depart from this curve. Combustionmainly takes place during the rising pressure portion 210 of the cycleand a negative pressure portion 220 of the cycle follows. During thenegative pressure portion 220, air and fuel enter the combustion chamber22 through the inlet 26 (FIG. 2). Although the combustion mainly occursduring the positive portion 210 of the cycle, some combustion lingers onduring the negative pressure portion when the combustor is warm,especially near the wall of the combustion chamber 22, perhaps due toboundary layer effect. Once the pressure rises, the fresh air/fuelmixture present in the combustion chamber 22 is ignited by the boundarylayer and combustion or more precisely, an explosion occurs. The energydeployed by the cyclic explosions adds to the resonance frequency of theresonator and helps sustain this resonance in a manner similar to howthe edge-tone principle generates energy which contributes to sustainthe resonance in some musical wind instruments.

To maintain a satisfactory flow of air and fuel into the combustionchamber 22, it is desired that the velocity impulse from the positivepressure pulses 210 of the explosion be guided to exhaust through theexhaust pipe 24 rather than through the intake system 14. One way tocontribute to this goal is to augment the ejecting action of the ejectorand to use the momentum of fuel and air in the first tube 40 and secondtube 42 to counter the pressure pulses exiting the intake tube 36. Inthe following discussion, this way, and other ways to contribute to thisgoal will be discussed.

To reduce the travel of the pressure pulses or waves through the inlet26 and intake system 14 at the pulsating frequency, it is desired toincrease the intake system impedance at that frequency. One skilled inthe art of acoustics is aware of basic acoustic filter theory and willrecall that an acoustic high-pass filter can be constructed using a Tjunction or a side-branch opening in a duct or pipe. If both the radiusand the length of the side branch are smaller than a wavelength of theplane waves in the duct then the acoustic impedance of the side-branchopening becomes a function of the side-branch opening area and of theside-branch length.

Turning back to FIG. 3, it is seen that in the intake system 14 (FIG.2), the intake tube coupling 148 includes an adjustment of penetrationdepth and area difference. Although the visual appearance of thecoupling 148 between these tubes is much different from the appearanceof a side branch in a straight pipe, it was found that the acousticbehaviour is actually quite similar, with the difference of area betweenthe second tube and the intake tube being equivalent to the opening areaof the side branch, and the penetration depth of the second tube intothe intake tube being equivalent to the length of the side branch. Thecoupling 148 between the second tube and the intake tube can thereforeact as a precisely selected high-pass filter 114 if the penetrationdepth and the difference of area are precisely chosen. A similardiscussion can be made of the coupling 146 between the first tube 140and the second tube 142. In FIGS. 5A and 5B, the penetration depth 160of the first tube 140 into the second tube 142 and the difference ofarea 162 between the first tube 140 and second tube 142 are identifiedfor further clarity.

Referring to FIGS. 5A and 5B, it will be discussed how to enhance theejecting action of the ejector system 118. A first point which may bemade is that as it is known to those skilled in the art of fluidmechanics, a well rounded inlet creates less energy loss and eases thepenetration of fluid relatively to a sharp edged inlet. This phenomenonis used advantageously in the case of the first and second tubes (140,142) which have rounded inlets (140 a, 142 a) and straight edge outlets(140 b, 142 b). Hence the impedance to a flow of air is greater whentraveling into the outlet than when traveling into the inlet, and thuscontributes to enhance the ejecting action.

One parameter to consider when adjusting the ejecting action of theejector system 118 is the adjustment of the position of the nozzle 138relative to the first tube inlet 140 a. Typically, a small gap will bepresent between the nozzle 138 and the first tube inlet 140 a. One cancontemplate the effect of the position of the nozzle 138 by monitoringthe amount of fluids ejected from the second tube outlet 142 b.

Furthermore, it will be understood that the first tube 140 and thesecond tube 142 act as open ended cylinders acoustically and that assuch, they have a fundamental resonance frequency which is a function ofthe length of the tube in addition to being a function of the speed ofsound. However, the diameter of the tube does not have much influence onthe acoustics. For aerodynamic, fluid mixing and momentumconsiderations, the second tube will generally be chosen to be longerthan the first tube and will therefore have a lower fundamentalfrequency. It was found that most supersonic fluid nozzles (which arefuel nozzles when the ejector system 18 is used with the pulse combustor10) generate pressure vibrations while they inject fluid. Of threepossible fluid nozzle types, both the over-expanded and under-expandedtypes produce pressure vibrations. It was found that when using atypical over-expanded nozzle, high amplitude and high frequency pressurewaves (or noise) resulted which excited the first tube 140 intoresonance. In turn, the resonance of the first tube 140 enhanced theejecting action of the first tube. The fluid nozzle 138 therefore actedas a high-frequency noise generator having a frequency and amplitudesuitable to acoustically excite the first tube 140. It was found that byselecting a first tube 140 having a fundamental resonance frequencywhich was a harmonic of the second tube fundamental resonance frequency,the resonance of the first tube 140 was transmitted to the second tube142 and excited the second tube 142 into resonance. In the tests, thefirst tube fundamental resonance frequency were selected to be the thirdharmonic of the second tube fundamental resonance frequency. Theresonance of the second tube 142 further enhanced the ejecting action ofthe injector.

Similarly, if a third tube is coupled to the second tube, such as anintake tube for example, the resonance frequency of the third tube canbe selected to be in tune with the resonance frequency of the secondtube.

In this specification, the term sub-harmonic is used to designate theinverse of a harmonic. For example, if the first tube has a fundamentalresonance frequency which is the third harmonic of the second tubefundamental resonance frequency, the second tube fundamental resonancefrequency can be said to be at the third sub-harmonic of the first tubefundamental resonance frequency. The expression in tune indicates thatthe resonance frequency of a first element is either the same, aharmonic of, or a sub-harmonic of the resonance frequency of a secondelement.

Comparing FIGS. 2 and 3, another acoustic component which mayadvantageously be used with the combustor 10 is to use a combustionchamber 22 shaped to act as an oscillator 122. The nose-cone 30 of thecombustion chamber 22 acts as a same-phase reflector 130 to the acousticpressure wave caused by the explosion. Furthermore, using the nose cone30 shape instead of a flat end is advantageous because it flattens outthe incoming pressure wave, diminishing the amplitude and increasing theperiod with the reflection. The converging section 32 of the combustionchamber 22 acts as a partial inverse-phase reflector 132 which reflectsa portion of the outgoing pressure wave back into the oscillator 122with the opposite phase. The combined action of the reflector 130 andthe partial reflector 132 is to trap and magnify a frequency which ishigher than the pulsating frequency in the oscillator 122. Theoscillator 122 can thus be said to also have its own fundamentalresonance frequency. By adjusting the length of the oscillator 122taking into account the speed of sound at operating temperatures, thefundamental resonance frequency of the oscillator 122 can be selected tobe a harmonic of the pulsating frequency of the resonator 112. Due tothe closed-end cylinder acoustic characteristics of the resonator 112,the odd harmonics are favoured. Typically the third harmonic isselected, although it will be understood that another harmonic such asthe fifth harmonic can also be selected.

In FIG. 4, an exemplary sinusoidal curve 230 representing the oscillator122 resonating at the third harmonic of the pulsating frequency 200 isshown, although it will be understood that the actual pressure curve maydepart somewhat dramatically from this sinusoidal curve illustration. Inthe combustion chamber 22, the pulsating frequency 200 and theoscillator frequency 230 are superposed, which gives rise to a resultingcurve which has a more complex form. Other harmonic frequencies andnoise are also present in an actual pulse combustor 10 during operation.

The resonator 1 12 therefore acts as a low-pass filter 112 a allowingthe pressure waves at the pulsating frequency out of the combustionchamber 22 and through the exhaust pipe 24, but at least partiallymaintains the pressure waves at the oscillator resonance frequency inthe oscillator 122. The cut-off frequency of this low-pass filter 112 acan be said to be between the pulsating frequency and the oscillatorfrequency.

The oscillator 122 can also be said to have an acoustic center 123 wherethe oscillator pressure variations are optimized. This acoustic center123 may somewhat depart from the longitudinal center of the combustionchamber. For instance, if a gas fuel is used and a coil 50 is present inthe aft portion (32) of the combustion chamber 22, the coil 50 willdecrease the mean temperature in that portion of the combustion chamber22, therefore lowering the speed of sound in that portion relatively tothe fore portion (30) of the combustion chamber 22. As a result, theacoustic center 123 will be shifted toward the fore portion of thecombustion chamber 22 relatively to the longitudinal center.

It is understood that the intake tube 36 can be seen from one acousticperspective as an open cylinder resonator. The diameter and the lengthof the intake tube 36 are guided by aerodynamic, thermodynamic andmomentum considerations. However, it has been found that by using anintake tube having a length giving a fundamental resonance frequencywhich is equal to the oscillator resonance frequency or a harmonicthereof results in the oscillator driving the resonance of the intaketube. Furthermore, the length of the equivalent acoustic cylinder formedbetween the nose cone tip and the intake tube outlet, and the length ofthe equivalent acoustic cylinder formed between the small end of theconverging section and the intake tube outlet are chosen to haveacoustic resonance frequencies which are harmonics of the pulsatingfrequency.

The resonance of the intake tube 36 contributes to maximize the ejectingaction of the ejector 18. To maximize the resonance-driving effect ofthe oscillator 112, the penetration depth and the area differencedefining the acoustic coupling 148 between the second tube 142 and theintake tube 136 and the acoustic coupling 146 between the first tube 140and the second tube 142, can be selected to create a high-pass filter114 in which the cut-off frequency is between the pulsating frequency ofthe resonator 112 and the resonance frequency of the oscillator 122.Another factor to influence the resonance-driving effect of theoscillator 122 is to place the combustion chamber inlet 26 (therebyplacing the intake tube outlet 36 b) at the longitudinal acoustic center123 of the oscillator/combustion chamber.

Another factor in increasing the acoustic impedance of the intake tube36 to the pressure pulses from the explosions in the combustion chamberis to give a funnel shape to the intake tube 36 by making it aconverging section with the larger end acting as the outlet 36 b andbeing connected to the combustion chamber inlet 26.

The result is that the arrangement of acoustic components as shown inFIG. 3 defines an acoustic cavity 110 which can advantageously be usedin a pulse combustor 10 because the resonance frequencies can be chosenin a manner in which they interact during combustor operation to obtainincreased combustor efficiency, power or thrust.

Typically, when the combustor 10 is started, the temperature of thecombustion chamber 22, intake tube 36 and exhaust pipe 24 are below thenormal operating temperatures, and the resonance frequencies will be outof tune. The combustor will start with a lower power output until thecomponents are heated up and a steady-state regime is reached andsustained.

Turning now to FIG. 6, an example of another configuration of acombustor 310 is shown, which will be referred to herein as the “in-lineconfiguration”. For clarity, this in-line combustor 310 will bedescribed using reference numerals in the three hundred series.Similarly to the L-shape pulse combustor 10 shown in FIG. 1, the in-linecombustor 310 also includes a body 312 generally disposed on a main axis316 and an intake system 314 disposed on an intake axis 320. However, inthe case of this in-line combustor 310, the intake axis 320 and the mainaxis 316 coincide and the intake system 314 is oriented away from thebody 312 in a direction opposite from the direction of the exhaust pipe324. As it will be understood, this in-line configuration procures somesignificant advantages relative to the L-shape configuration, especiallywhen the combustor is used as an engine for propulsion, rather than as aburner for hot air generation.

In FIG. 6, the in-line combustor 310 uses gaseous fuel as it can beunderstood from the fuel line 356 which extends between the fuel nozzle338 and a coil (not shown) in the combustion chamber 322. This featureis similar to the features illustrated in FIG. 2. However, it will beunderstood that a liquid fuel can also be used and that the coil can beomitted. For simplicity, this latter case is illustrated in FIGS. 7 and8.

Referring to FIGS. 6, 7 and 8, it can be seen that at least some of thestructural and acoustic components of the in-line combustor 310 areequivalent to the structural and acoustic components of the L-shapedpulse combustor 10 illustrated in FIGS. 1, 2 and 3, without limiting theadvantages of this in-line configuration in terms of performance andadditional capabilities. For the sake of clarity and simplicity, thein-line combustor example will therefore be described on the basis ofcomparisons made relative to the L-shape pulse combustor 10 example.

Like the L-shape pulse combustor 10, the in-line combustor 310 alsoincludes a body 312 which has a combustion chamber 322 connected to anexhaust pipe 324, with an outlet 328 in the exhaust pipe 324 and aninlet 326 in the combustion chamber 322. However, in this example, theinlet 326 is peripheral to the combustion chamber 322 instead of beingan aperture 26 on one side of the combustion chamber 22 as was the casefor the L-shape combustor 10.

Furthermore, like in the case of the L-shape combustor 10 example, thein-line intake system 314 also basically functions on the principle ofan ejector and includes an ejector system 318 with a supersonic fuelnozzle 338, a first tube 340 and a second tube 342. Instead of beingsimply cylindrical, the second tube 342 has a cylindrical portion 341and a flared end portion 343 which covers a portion of the nose cone330. The cross-sectional area defined between the nose cone 330 and theflared portion 343 is substantially equal to the cross-sectional area ofthe cylindrical portion 341. The intake system 314 also includes anintake tube 336, but the intake tube 336 in this case has the shape of acowl that covers the portion of the combustion chamber 322 extendingfrom the peripheral inlet 326 and the outlet 342 b of the second tube342. The cross-sectional area between the combustion chamber 322 and theintake tube 336 can be chosen to be equivalent to the cross-sectionalarea of the cylindrical intake tube 36 which was used in the L-shapecombustor example (FIG. 1), for example. In this case, the intake tube336 overlaps a portion of the second tube 342, and it will be understoodthat this overlap distance equates the penetration distance 160 (FIGS.5A and 5B) and can be selected together with the area difference 162 toachieve desired filtering characteristics, as can be seen from thediscussion above.

One skilled in the art will understand that the choice of the irregularshape of the second tube 342 and intake tube 336 has only a minimalinfluence on the acoustic, aerodynamic and momentum characteristics ofthese components. These irregular shapes are a good example of how thestructural shape of certain components of the combustors 10, 110, 310can be greatly varied while not substantially affecting their functionin combustor operation. This should serve as an illustration of how thereader of the instant specification must bear in mind the essentialacoustic, aerodynamic and/or momentum characteristics of the combustorcomponents rather than to only look at the simple structuralcharacteristics or visual appearance of the combustor components.

One special feature of the in-line configuration is that the intakesystem 314 can benefit from the effect of ram air when the engine isdisplaced in the surrounding air. During engine displacement,surrounding air is “caught” in the area between the fuel nozzle 338 andthe first tube 340, in the area between the first tube 340 and thesecond tube 342, and the area between the second tube 342 and the intaketube 336. This ram air increases the amount of air flow through theintake system 314, which opposes the direction of the pressure pulses inthe intake tube 336. This ram air can thus be used to increase combustorefficiency.

When ram air is used with the intake system 314, the combustor 310 canenter a mode which will be referred to herein as the ram mode. Duringthe transition to the ram mode, the pulsating frequency can vary. In theram mode, the acoustic considerations can become of lesser importancerelatively to other aerodynamic and thermodynamic considerations.

Referring now to FIGS. 9A to 9E, discussion will be made of theperipheral inlet to the combustion chamber. One will understand thatwhen designing the inlet (26 or 326 for example) of a combustor, oneattempts to satisfy various requirements. First, the inlet should have asufficient overall size (area) so as to allow a satisfying amount of airand fuel to flow into the combustion chamber. To enhance the acousticinteraction between the intake tube and the oscillator as was discussedabove, the inlet should have a sufficient longitudinal length to allowthe longitudinal waves reflected from the reflector and the partialreflector to form appropriate waves in the intake tube. Furthermore, onedoes not wish that the overall area defined by the combustion chamberinlet be too important because this has the effect of lowering theimpedance of the intake tube to the pressure pulses from the pulsatingfrequency and consequently increases the amount of discharge through theintake tube at the expense of the amount of thrust or hot air dischargethrough the exhaust pipe.

To satisfy the requirement of inlet overall size and inlet longitudinallength along the combustion chamber discussed above, it has been foundadvantageous to provide the inlet 326 as a plurality of apertures. Inthis example, the apertures are slots 327 which are tangentiallyinterspaced around the combustion chamber wall relative to the main axis316 (FIG. 6). The slots 327 can be longitudinally oriented to optimizetheir actual longitudinal length. Alternately, they can be somewhatangled. Further, to maximize the acoustic interaction between the intaketube 336 and the oscillator 122 formed by the combustion chamber 322,the slots 327 can be longitudinally positioned at the acoustic center323 of the oscillator. The main acoustic length of the intake tube 336can then be calculated from the inlet 336 a to the nearest end 327 a ofthe longitudinal slots 327. In other examples, the apertures can beprovided as tangentially spaced sets of longitudinally alignedapertures, or in other aperture configurations which are not necessarilylongitudinally aligned but which satisfy similar acoustic andaerodynamic criteria.

One way to further enhance intake flow through the slots 327 and toreduce backflow from the combustion chamber 322 is to provide the slotswith a rounded edge 327 b which penetrates into the combustion chamber322. This is more clearly shown in FIGS. 9B and 9C. The backflow is thusfaced to a re-entrant edge having a high loss coefficient, whereas theintake flow faces a rounded edge having a low loss coefficient. Flowinto the combustion chamber 322 is thus favoured relative to backflow.This configuration can be realized in sheet metal by punching the slots327 in prior to rolling the cylindrical section 334 of the combustionchamber 322, for example.

In the example illustrated in FIGS. 9A to 9C, the rounded edges of theslots are oriented generally perpendicularly to the combustion chamberwall or to the combustor central axis.

However, it will be understood that to favour a vortex flow, the roundededges of the slots can be tangentially slanted relatively to thecombustion chamber wall or the central axis, in a common tangentialdirection, such as the slots 427 shown in FIG. 9D for example. Thischanges the configuration of the penetrating flow of fuel and air, andcan increase the resistance to backflow. In FIG. 9E, it is shown thatthe slots 427 can also have edges which are longitudinally slanted.

Referring to FIG. 10, it can be seen that in this example of an in-linecombustor 310, the intake system 314 is held into position by aplurality of fins 370, 372, 374. In the example, four fins are usedbetween each two components. The fins 370, 372, 374 are longitudinallyoriented and are made thin in order to minimize their resistance toinflowing air. For the first tube coupling 344, first tube fins 370connect the first tube inlet 340 a to the nozzle 338. For the secondtube coupling 346, second tube fins 372 connect the second tube inlet342 a to the first tube 140. For the intake tube coupling 348, intaketube fins 374 connect the intake tube inlet 336 a to the flared endportion 343 of the second tube 342. The end 337 of the intake tube 336can be welded directly to the combustion chamber 322, slightly past thefar end 327 b of the slots 327. The penetration depth 360 a of the firsttube into the second tube and the penetration depth 360 b of the secondtube into the intake tube are also identified. If the intake system 314is made of metal tubes and nozzle, the fins can be affixed by welding.It will be understood that this latter structural configuration is anexample only and that many other ways to hold the components of theintake system into operating position can alternately be used.

Turning now to FIG. 11A to 11C, an alternate configuration of acombustor 510 is shown. In this example, the combustion chamber 522 alsohas a plurality of apertures interspaced near an acoustic centerthereof, and in this case, the apertures are also longitudinallyoriented slots 527. The slots 527 also define an inlet 526 to thecombustion chamber 522 and the intake system 514 is connected to thisinlet 526. However, in this configuration, the slots 527 are disposedaround the intake tube 536, and the intake tube 536 penetrates into thecombustion chamber 522. In the illustrated configurations, the intaketube 536 has a closed end. In FIG. 11B, the closed end is a flat end529, whereas in FIG. 11C, the closed end is a rounded end 531. In theseexamples, the intake system 514 is aligned with the axis of the body 512and is oriented opposite the tail pipe 524. The combustion chamber 522has a flat front end 530 instead of the nose cone shown in the precedingexamples. The flat front end 530 bridges and closes the opening betweenthe end of the straight section 534 and the intake tube 536.

Turning now to FIG. 12, a schematic view of a turbine system 600 torecuperate energy from the hot gasses exhausted by in-line combustors610 is shown. The combustors 610 are aligned with their axes beingcircumferentially interspaced around a central axis 605. A power turbine680 is positioned at the outlet 628 of the in-line combustor exhaustpipes 624. A fan 682 is positioned ahead of the in-line combustor intakesystems 614 and is connected to the power turbine 680 by a shaft 684along the central axis 605. In operation, the power turbine 680 rotatesby extracting power from the combustion gasses and transmits therotation to the fan 682 via the shaft 684. The fan 682 thus generates astream of air which adds to the ejecting action of the ejector system618 and increases the flow of air into the combustion chamber 622. Otherturbine-based systems to recuperate energy from the combustion gases mayalternately be used as well.

It shall be noted here that although combustors having generallycylindrical bodies were described above, other shapes can be usedinstead. For example, the combustion chamber and body can be made with agenerally ellipsoidal cross-section in order to make them somewhatflatter. Further, although the use of the slotted intake was foundsatisfying in the in-line combustor described above, other types ofapertures can be used instead. In one alternate embodiment, an annularslot making the entire periphery of the combustion chamber can be usedinstead of the plurality of slots. In a case where the combustionchamber has an ellipsoidal cross-section, a separate aperture on eachrespective flat side of the combustion chamber can be used instead ofthe plurality of slots, for example.

Further, although an intake system using three stages defined by thefirst tube, second tube and intake tube was used in the examples above,it is to be understood that a different number of stages can also beused.

The ejector system described above can be used in other applicationsthan in an intake system. It can also be used in other types of intakesystems. For example, in FIG. 13, an ejector system 718 is shown on anengine known as the Hiller-Lockwood engine 710.

In the tests, combustors were made of steel. However, other materialscan be used as well. One consideration is that the materials used havesuitable acoustic properties. One other consideration is that thematerials used have sufficient resistance to heat, especially for thecombustion chamber and exhaust pipe.

In the example given above, the ejector system was used to eject a mixof fuel and air and was made part of an intake system of a combustor.However, it is believed that many other applications can also be made tothe acoustically enhanced ejector system. It can be used with fluidnozzles which inject other types of fluids which may or may not be fuel,and with different ambient fluids. In the examples given above, theinjected fluid was fuel and the ambient fluid was air.

It will be noted that other types of intake systems can be used to feedfuel and air to a combustor having an oscillator at a resonancefrequency which is an odd harmonic of the pulsating frequency.

It will be understood that the overall size and shape of the combustorsdescribed and illustrated above can be varied to generate a combustorwhich is adapted to a specific application.

As can be seen therefore, the examples described above and illustratedare intended to be exemplary only. Hence, the scope of the improvementsis intended to be limited solely by the scope of the appended claims.

1. A combustor comprising: a tubular combustor body, the body having: a combustion chamber having a plurality of tangentially spaced apertures wherein the apertures are disposed around an intake tube which protrudes into the combustion chamber; an exhaust pipe narrower than the combustion chamber and extending away from the combustion chamber and being in flow communication therewith, the exhaust pipe defining an outlet of the tubular combustor body; and an intake system in fluid communication with the apertures to feed the combustion chamber with fuel and air that has passed through the apertures and into the combustion chamber.
 2. The combustor of claim 1 wherein the apertures are longitudinally oriented slots.
 3. The combustor of claim 2 wherein the slots have a rounded edge defining a re-entrant edge in the combustion chamber.
 4. The combustor of claim 3 wherein the edges of the slots are tangentially slanted.
 5. The combustor of claim 1 wherein the intake system includes: a supersonic fuel injection nozzle having an acoustic injection frequency; a first resonant tube having an inlet coupled to the nozzle for receiving injected fluid from the nozzle and ambient fluid entrained by the injected fluid, and an outlet for ejecting the fluids, the first resonant tube having a first fundamental resonance frequency excitable by the nozzle; a second resonant tube having an inlet coupled to receive the fluids ejected from the first resonant tube outlet and additional ambient fluid entrained by the ejected fluids, and an outlet for ejecting fluids received by the inlet, the second resonant tube having a second fundamental resonance frequency; and a resonant intake tube having an inlet coupled to the outlet of the second resonant tube for receiving the fluids ejected from the second resonant tube outlet and additional ambient fluid entrained by these ejected fluids, and an outlet connected to the apertures.
 6. The combustor of claim 5 wherein the second fundamental resonance frequency is a sub-harmonic of the first fundamental resonance frequency. 